In the tumultuous backdrop of 17th Century France, the ambitious Cardinal Richelieu (Christopher Logue) is weaving a complex web of deceit and manipulation, seeking to extend his grasp on power by influencing King Louis XIII (Graham Armitage). Engaging the king in persuasive dialogues, Richelieu successfully convinces him that the fortifications of cities across France should be dismantled to thwart any potential Protestant uprisings. However, the king, bound by a promise to protect the town of Loudun, forbids the demolitions there.
As circumstances unfold in Loudun, the recent death of its Governor hands control over the town to Urbain Grandier (Oliver Reed), a charismatic yet indulgent Catholic priest, renowned for his community standing. Grandier, engaged in a clandestine affair with a relative of Father Canon Mignon (Murray Melvin), finds himself oblivious to the obsessive infatuation held by a deformed and neurotic nun, Sister Jeanne (Vanessa Redgrave), who fervently desires him as the convent's new confessor. In a private ceremony, Grandier marries Madeline De Brou (Gemma Jones), yet the veil of secrecy is soon lifted, sending Sister Jeanne spiraling into a tempest of jealousy and madness.
This turmoil culminates in a vicious confrontation where Sister Jeanne, in a fit of rage, attacks Madeleine, branding her a "fornicator" and a "sacrilegious bitch." Reinforcements for the disruption arrive in the form of Baron de Laubardemont (Dudley Sutton), who brazenly flouts Grandier's authority to carry out the king's orders for the city's demolition. In a bold stand, Grandier rallies the local soldiers to thwart Laubardemont temporarily, until he sets off to petition the King directly for support.
Meanwhile, Sister Jeanne, misled by Father Mignon, proxies accusations against Grandier of witchcraft after her learning of his marriage. The information, distorted and exaggerated as it travels, transforms into a sensational claim that Grandier has bewitched the convent, igniting a frenzy of hysteria among the nuns. With Grandier absent, Laubardemont seizes the opportunity to concoct evidence of alleged sorcery.
In a shocking twist of fate, Laubardemont enlists the notorious inquisitor Father Pierre Barre (Michael Gothard), a zealot notorious for his cruel methodologies, compounded by depraved exorcism practices. The nuns, led by Sister Jeanne, come forward with accusations claiming that Grandier's dark magic has ensnared them in sin. What ensues is a grotesque public exorcism, spiraling into chaos as the nuns, caught in religious tumult, strip and indulge in frenzied behaviors, besmirching both their sanctity and the decency of a holy communion.
The intervention of Duke Henri de Condé (who is, unbeknownst to many, a disguised King Louis) adds another layer of intrigue. Promising to exorcise the alleged devils possessing the nuns, he introduces a holy relic, only for it to be revealed later as an empty vessel, clearly exposing the charade of possessions to the townsfolk. But, unyielding in their paranoia and lust for vengeance, the witch-hunt escalates into a violent orgy of blasphemy as the nuns attack a statue of Christ.
As the layers of deception peel away, Grandier and his wife inevitably return to town, leading to his immediate arrest. The farcical nature of justice spills forth in a mock trial, where Grandier is subjected to brutal torture, yet miraculously manages to reaffirm his innocence to Mignon, who grapples with his waning sanity. Nevertheless, the judgment is swift and merciless; under the heavy hand of Laubardemont, Grandier is sentenced to a horrific execution—burning at the stake.
Even amidst the harrowing ordeal, Grandier's steadfast refusal to admit guilt adds gravity to his plight. As flames encroach upon him, Barre's fanatical fervor turns the execution into a spectacle of horror, culminating in an explosion that demolishes the city’s defenses and sends its inhabitants into chaos. In a moment of tragedy, Mignon, tormented by doubt, miscalculates and tightens the noose around Grandier’s neck before he can meet a more merciful end.
With the city’s fall into disrepair and disillusionment following Grandier's fiery end, Sister Jeanne is left in shambles, her lust now twisted into a mournful obsession as she engages in a grotesque act with a charred remnant of Grandier. Meanwhile, Grandier's widow, bestowed with freedom amid the ruins, steals away from the city—a haunting testament to the dark ramifications of power and obsession, wrapping the narrative in an unsettling silence as the echoes of tragedy reverberate into the lingering dusk.
